Zero volume rocket ignition system

ABSTRACT

A rocket ignition system for artillery fired projectiles has a fixed nozzle design which permits maximum propellant loading by interposing a high density, low residue, heat buring paper intermediate a nozzle end plate and a solid propellant. An initiating squib prior to launch temporarily closes off the nozzle orifice from the hot breech gases. After launch the squib initiates a mild detonating fuze which burns the heat paper and ignites the propellant causing generation of gases whose pressure causes expulsion of the nozzle-squib plug from the nozzle orifice. In a movable nozzle embodiment an initiating train is fixedly held, prior to launch, in a slidable nozzle member adjacent to an igniter pellet charge which activates the propellant. Interposed between the movable nozzle and the propellant grain is an integrally cast liner which excludes all air from the propellant grain surface thus preventing premature ignition of the propellant by gun breech compressed gases.

tlite tates tent [1 1 Mertens et al.

ZERO VOLUME ROCKET IGNITION SYSTEM [75] Inventors: Robert C. Mertens, Rancho Cordova; Donald W. Harper, Roseville, both of Calif.

[73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC. [22] Filed: Aug. 30, 1973 [21] Appl. No.: 393,240

[52] US. Cl. 102/49.7, 60/256 [51] Int. Cl. F42!) 13/28 [58] Field of Search 89/18, 1.818; l02/49.3, 102/49.7, 70; 244/328; 60/256 [56] References Cited UNITED STATES PATENTS 2,552,497 8/1951 Roach et al 102/49.3 X 2,613,604 10/1952 Pyle 102/49.7 X 3,104,523 9/1963 ODonnelL. 60/255 3,404,532 10/1968 Olstein 102/49 7 3,434,419 3/1969 Dimond et al 102/493 3,667,396 6/1972 Barrett l02/49.7 X FOREIGN PATENTS OR APPLICATIONS 976,483 11/1964 Great Britain 244/328 Primary Examiner-Samuel W. Engle Attorney, Agent, or Firm-Edward J. Kelly; Herbert Berl; Thomas R. Webb [5 7] ABSTRACT A rocket ignition system for artillery fired projectiles has a fixed nozzle design which permits maximum propellant loading by interposing a high density, low residue, heat buring paper intermediate a nozzle end plate and a solid propellant. An initiating squib prior to launch temporarily closes off the nozzle orifice from the hot breech gases. After launch the squib initiates a mild detonating fuze which burns the heat paper and ignites the propellant causing generation of gases whose pressure causes expulsion of the nozzle-squib plug from the nozzle orifice. In a movable nozzle embodiment an initiating train is fixedly held, prior to launch, in a slidable nozzle member adjacent to an igniter pellet charge which activates the propellant. Interposed between the movable nozzle and the propellant grain is an integrally cast liner which excludes all air from the propellant grain surface thus preventing premature ignition of the propellant by gun breech compressed gases.

2 Claims, 4 Drawing Figures Pmemm 3,861,310

' sum 20F 2 ZERO VOLUME ROCKET IGNITION SYSTEM GOVERNMENTAL INTEREST The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.

BACKGROUND OF THE INVENTION Various means have been used in prior art to get the maximum propellant loading into minimum projectile space or envelope. It is important to obtain the maximum propellant loading for minimum space in an artillery launched rocket type projectile in order to in crease either the range of the projectile or the size of the warhead for improved lethality.

Prior art conventional rocket motors have had problems with inadvertent premature ignition of the propellant grain from too rapid external pressurization. Some of the prior art devices have tried to overcome the maximum propellant loading problems by the use of lightweight case materials, increasing propellant density, submerged nozzle design, and internal grain design. For prevention of gas compression and premature ignition heavyweight or beefed-up construction is generally required for the fixed nozzle design. For the movable nozzle design, prior art devices have had to use hard-toignite propellant grains to solve the premature ignition from gas compression. All of the aforementioned solutions are unsatisfactory because they result in either reduced safety, reduced lethality, and/or in shorter operative projectile range. Heavyweight construction defeats the overall goal of maximum propellant loading since inert weight (W becomes excessive and mass fraction (M.F.) decreases for a given propellant weight (W according to the relation:

WP W! tmotur) Use of hard-to-ignite propellant is unsatisfactory since the complexities of the motor system are increased in order to assure reliable ignition of this type of propellant.

SUMMARY OF THE INVENTION The present device relates to a fixed or movable nozzle zero volume rocket ignition system which permits maximum propellant loading into minimum space and eliminates premature grain ignition of the rocket propellant by igniter cavity gases. In the fixed nozzle design an initiating squib, which temporarily blocks the nozzle orifice, initiates a mild detonating fuze which is operatively spaced intermediate a nozzle plate member and the solid propellant. The nozzle plug is expelled during ignition of the propellant. In the alternate embodiment, the movable nozzle zero volume ignition design, ignition of the propellant is accomplished when a pyrotechnic train fires an igniter pellet charge. The gases generated by the ignition of the propellant push a movable plugged nozzle plate member away from the propellant a fixed distance and as a result of the continued build up of pressure the gas blows out the nozzle plug expelling gases from the now open nozzle thereby giving the launched projectile additional rocket thrust. Use of the movable nozzle plate member allows the rocket motor wall to be made substantially thinner and thereby lighter by utilizing movement of the nozzle plate member or closure against the propellant grain during firing to provide an internal hydrostatic pressure to offset, in part, the external pressure generated in the gun chamber during firing. The movable nozzle plate member with its temporarily closed nozzle eliminates any free volume within the motor body which may contain heat generating gases which could inadvertently ignite the propellant grain during gun firing.

One of the objects of the present invention is to provide an artillery fired rocket projectile with a zero volume ignition system.

Another object of the present invention is to provide an artillery fired rocket projectile having a zero volume ignition system with a fixed nozzle arrangement.

Another object of the present invention is to provide an artillery fired rocket projectile having a zero volume ignition system with a movable nozzle arrangement.

Another object of the present invention is to provide an artillery fired rocket projectile having a zero volume ignition system for maximum propellant loading for minimum space.

Another object of the present invention is to provide an artillery fired rocket projectile having a zero volume ignition system which will not cause inadvertent premature ignition of the propellant grain.

Another object of the present invention is to provide the lethality of artillery fired rocket projectiles.

A further object of the present invention is to provide an increase in the effective range of artillery fired rocket projectiles.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial axial cross-sectional view of the fixed nozzle, zero volume rocket ignition system.

FIG. 2 is a rear end view taken along line 22 as illustrated in FIG. 1.

FIG. 3 is a partial axial cross-sectional view of the movable nozzle, zero volume rocket ignition system.

FIG. 4 is a rear end view taken along line 4-4 of the movable nozzle embodiment as illustrated in FIG. 3.

Throughout the following description like reference numerals are used to denote like parts of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2, rocket motor 10 is affixed to the end of an artillery projectile, not shown, by means of threaded boss 12. the rocket motor housing 14 has rotating bands 16 circumferentially positioned about housing 14 intermediate front boss 12 and the rocket motor rear end 18. A solid propellant 20 totally fills the rocket housing cavity 26 formed between the boss rear end 24 anda disc shaped rear heat paper 26 so that there are no voids therebetween. A circular, disc shaped, nozzle plate member 28 is fixedly held within the open end 15 of motor housing 14 by a retainer ring 30, which is are welded at weld 31 to housing 14, so that plate member front face 32 is tightly held against a front annularly disc shaped front heat paper 34. A spirally shaped mild detonating fuze train 36 is operatively positioned intermediate the front and rear heat papers 34 and 26 respectively. The disc shaped nozzle plate member 28 has an integrally formed axially aligned nozzle 38 formed on its rear face 35 and a silver infiltrated tungsten insert 39 in its front face 32 in combination therewith, the latter helps nozzle 38 resist nozzle erosion. Prior to projectile launch the nozzle 38 is partially filled and closed with a pressure releasable nozzle plug 40. Axially aligned and threadedly positioned in the nozzle plug 40 is an initiating squib 42 whose output communicates through squib fire channel 44 to the inner front end 46 of the detonating fuze. An ring assembly 48 is annularly located in the circumferentially positioned 0" ring groove 50. The O ring assembly 48 helps in preventing premature ignition of the propellant grain by isolating the hot compressed breech gases from the propellant during the launch phase of the projectile.

Referring now to FIGS. 3 and 4, a movable nozzle plate member 52 is slidably positioned in the motor housing 14 and biasedly held therein by a spring 53. The plate member 52 is fixedly held from slipping out of the rocket motor rear end 18 by an externally threaded retainer ring 54. In the plate member rear surface 71 a pyrotechnic train 58 is threadedly held in the axial threaded plate member bore 60. Axially aligned with the pyrotechnic train 58 and centrally positioned in a rear propellant cavity 62 is an igniter pellet charge 64. A liner 68, made of material such as silica filled polyurethane, is precast and cured so that it seals off the propellant grain 66 to exclude air therefrom. A cup shaped insulator 70 for nozzle closure, made of material such as silica phenolic, is operatively positioned intermediate the front face nozzle plate member surface 72 and the liner 68. A plurality of equally spaced radially positioned nozzles 38, each having a silver infiltrated erosion resistant insert 41 therein, are integrally formed out of the movable nozzle plate member 52. A solid nozzle plug 74, made of such material as TEF- LON, partially fills the nozzle cavity 76, and is temporarily sealed therein by a plug sealant 78, such as a silicone incapsulating material type DC-30-l2l, manufactured by the Dow Corning Corp. of Midland, Mich., which is liquid when poured in the nozzle cavity 76 in the uncured state and solidifies upon air curing.

In operation, the fixed nozzle, zero volume ignition system, shown in FIGS. 1 and 2, is initiated by conventional electrical means applied to the initiating squib 42. When the squib 42 fires it ignites the mild detonating fuze 46 which in turn ignites the heat papers 26 and 34. The heat papers 26 and 34 burn without significant pressure generation, and leave a small space intermediate the plate member front face 32 and the solid propellant front end 33 at the time of ignition of the solid propellant 20. This small volume is needed to sustain the complete combustion of the propellant 20. The nozzle plug 40 is expelled after ignition of the propellant 20. Thus the combustion gases of the propellant 20 have a complete escape path whereas before ignition the rocket motor was completely sealed and no free volume or igniter cavity gases were present to cause premature ignition.

The mmovable nozzle zero volume system as shown in FIGS. 3 and 4 allows the heat papers 26 and 34 of the embodiment shown in FIG. 1 to be deleted. The free volume required for ignition and combustion gas escape is obtained from the movement of the movable nozzle plate member 52 toward the shoulder 56 of the threaded retainer ring 54 by the compression of spring 53 as pressurization occurs in the rocket housing cavity 22. Initiation of the pyrotechnic train 58 can be by gun breech pressure gases or by conventional electrical means. The igniter pellet charge 64 is in turn ignited by the pyrotechnic train 58. The pellet charge 64 then ignites the propellant grain 66. Gases generated by the igniter pellet charge 64 and the propellant grain 66 expel the nozzle plugs 74 as well as force the movable nozzle plate member 52 toward the retainer ring shoulder 56 thereby creating the necessary free volume needed to support rapid combustion of the propellant grain 66.

The foregoing disclosure and drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. We wish it to be understood that we do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled in the art.

Having thus fully described the invention, what is claimed as new and desired to be secured by letters patent of the United States is:

l. A zero volume rocket ignition system for an artillery launched projectile having an end-burning rocket motor which comprises:

a hollow cylindrically shaped housing having a closed threaded boss on its front end, for attachment to said projectile, and an open rear end; propellant means completely filling the major portion of said housing for maximum propellant loading; propellant igniting means operatively positioned immediately adjacent said propellant means; nozzle means positioned immediately adjacent said propellant igniting means and closing said propellant means in said housing thereby controlling thrust of said rocket motor after launch which includes; a disc shaped plate member having an integrally axially positioned nozzle protruding from its rear face; a silver infiltrated tungsten hollow nozzle insert operatively positioned in said plate members front face and axially aligned with said integral nozzle so as to form an erosion resistant nozzle orifice therein; a nozzle plug slidably positioned in the nozzle orifice of said integral nozzle and said nozzle insert; a retainer ring fixedly attached to the rear end of said housing and in peripheral abutment with the rear face of said plate member; and an O ring assembly annularly positioned in the circumferential edge of said plate member for preventing the venting of gases generated by said propellant means around the peripheral edge of said plate member and thereby reducing the thrust from said rocket motor; and wherein said propellant igniting means further includes; an initiating squib fixedly positioned in said nozzle means and communicating with a squib fire channel axially positioned in said nozzle means;

at least one heat paper positioned intermediate said nozzle means and said propellant means; and

a fuze train spirally positioned intermediate said heat paper and said nozzle means having its inner front end communicating with said initiating squib for igniting said heat paper after being initiated by said squib.

2. A zero volume ignition system for an artillery launched projectile having an end-burning rocket motor which comprises:

a hollow cylindrically shaped housing having a closed threaded boss on its front end, for attachment to said projectile, and an open rear end;

propellant means completely filling the major portion of said housing for maximum propellant loading which includes;

a propellant grain;

a liner, which includes silica filled polyurethane material, covering one end of said propellant grain;

propellant igniting means operatively positioned immediately adjacent said propellant means which includes;

a pyrotechnic train axially disposed in said rocket motor, said pyrotechnic train being initiated during launch;

an igniter pellet charge axially positioned immediately adjacent said propellant means and communicating with the output of said pyrotechnic train; and

nozzle means positioned immediately adjacent said propellant igniting means and closing said propellant means in said housing thereby controlling the thrust of said rocket motor after launch, which includes;

a movable disc shaped plate having a plurality of equally spaced integral nozzles protruding from the front surface of said plate member;

a plurality of silver infiltrated. tungsten hollow nozzle inserts operatively positioned in the front surface of said movable plate member and axially aligned with said integral nozzles forms erosion resistant nozzle orifices therein;

a plurality of nozzle plugs slidably positioned in said nozzles orifices;

a retainer ring fixedly attached to the rear end of said housing;

an O ring assembly annularly positioned in the circumferential edge of said movable plate member for preventing the venting of gases generated by said propellant means around the peripheral edge of said movable plate member; and

a spring interposed intermediate said retainer ring and said movable plate member for holding said movable plate member in close abutment to said propellant means prior to launch and for permitting said movable plate member to shift toward said retainer ring upon ignition of said pyrotechnic train and said propellant means so that a free volume required for sustained burning of said propellant means is obtained. 

1. A zero volume rocket ignition system for an artillery launched projectile having an end-burning rocket motor which comprises: a hollow cylindrically shaped housing having a closed threaded boss on its front end, for attachment to said projectile, and an open rear end; propellant means completely filling the major portion of said housing for maximum propellant loading; propellant igniting means operatively positioned immediately adjacent said propellant means; nozzle means positioned immediately adjacent said propellant igniting means and closing said propellant means in said housing thereby controlling thrust of said rocket motor after launch which includes; a disc shaped plate member having an integrally axially positioned nozzle protruding from its rear face; a silver infiltrated tungsten hollow nozzle insert operatively positioned in said plate member''s front face and axially aligned with said integral nozzle so as to form an erosion resistant nozzle orifice therein; a nozzle plug slidably positioned in the nozzle orifice of said integral nozzle and said nozzle insert; a retainer ring fixedly attached to the rear end of said housing and in peripheral abutment with the rear face of said plate member; and an ''''O'''' ring assembly annularly positioned in the circumferential edge of said plate member for preventing the venting of gases generated by said propellant means around the peripheral edge of said plate member and thereby reducing the thrust from said rocket motor; and wherein said propellant igniting means further includes; an initiating squib fixedly positioned in said nozzle means and communicating with a squib fire channel axially positioned in said nozzle means; at least one heat paper positioned intermediate said nozzle means and said propellant means; and a fuze train spirally positioned intermediate said heat paper and said nozzle means having its inner front end communicating with said initiating squib for igniting said heat paper after being initiated by said squib.
 2. A zero volume ignition system for an artillery launched projectile having an end-burning rocket motor which comprises: a hollow cylindrically shaped housing having a closed threaded boss on its front end, for attachment to said projectile, and an open rear end; propellant means completely filling the major portion of said housing for maximum propellant loading which includes; a propellant grain; a liner, which includes silica filled polyurethane material, covering one end of said propellant grain; propellant igniting means operatively positioned immediately adjacent said propellant means which includes; a pyrotechnic train axially disposed in said rocket motor, said pyrotechnic train being initiated during launch; an igniter pellet charge axially positioned immediately adjacent said propellant means and communicating with the output of said pyrotechnic train; and nozzle means positioned immediately adjacent said propellant igniting means aNd closing said propellant means in said housing thereby controlling the thrust of said rocket motor after launch, which includes; a movable disc shaped plate having a plurality of equally spaced integral nozzles protruding from the front surface of said plate member; a plurality of silver infiltrated tungsten hollow nozzle inserts operatively positioned in the front surface of said movable plate member and axially aligned with said integral nozzles forms erosion resistant nozzle orifices therein; a plurality of nozzle plugs slidably positioned in said nozzles orifices; a retainer ring fixedly attached to the rear end of said housing; an ''''O'''' ring assembly annularly positioned in the circumferential edge of said movable plate member for preventing the venting of gases generated by said propellant means around the peripheral edge of said movable plate member; and a spring interposed intermediate said retainer ring and said movable plate member for holding said movable plate member in close abutment to said propellant means prior to launch and for permitting said movable plate member to shift toward said retainer ring upon ignition of said pyrotechnic train and said propellant means so that a free volume required for sustained burning of said propellant means is obtained. 